An internal combustion engine is a combustion power machine which converts chemical energy of a fuel by combustion into mechanical work. The combustion takes place here in the combustion chamber, in which a mixture of fuel and ambient air is ignited. The thermal expansion of the combustion exhaust gas, which is hot through the combustion, is used in order to move a piston.
From the prior art in particular internal combustion engines are known which use up to 38.5% of the energy stored in the fuel for moving the piston. The remaining energy generated within the combustion—in the case of a cooled engine in addition to the cooling fluid—is discharged from the engine especially through escaping combustion exhaust gases. To reduce such heat losses, it was therefore proposed to supplement a generic internal combustion engine by a suitable heat recovery system.
Such a system typically uses a device designated as a heat transfer device, recuperator or heat exchanger, which transfers thermal energy from the combustion chamber of the engine to a heat carrier flowing around the latter. A problem here is the choice of the heat carrier, which is to be distinguished as such on the one hand by a high boiling point and heat transfer coefficient and high thermal capacity and conductivity, on the other hand by low viscosity, combustibility, toxicity and a low freezing point. Heat transfer devices known from the prior art therefore use, in addition to conventional cooling agents, for example water, ethanol, methanol, ammonia or mixtures based on these fluids as heat carrier.
Thus, for instance, U.S. 2008/0008605 A1 discloses a heat transfer device based on a pump, in which the movable part is a metal bellows, which is alternately filled with hydraulic fluid under high pressure and emptied. Here, the amount of fuel in the chamber in which the bellows moves is determined upstream by a magnet valve which is controlled by a computer for monitoring the engine. The proposed pump comprises at least two pump units which are supplied through a single inlet common to the two units.
FR 2 828 240-A1 also proposes a hydraulic pump for specific high pressure fluids such as petrol. Here, each cylinder of the hydraulic pump is connected on the one hand with a reservoir and on the other hand with a check valve, which selectively enter into fluid connection under the action of a distribution device controlled by means of a proportional magnet.
Finally, DE 103 06 146 A1 describes a low pressure reservoir for a high pressure piston pump for the pumping of fuel with a fluid-tight elastic separating structure, which has a first side and a second side, wherein the first side delimits a partial volume of the low pressure reservoir, which is connected hydraulically with a low pressure side of the high pressure piston pump. The low pressure reservoir is distinguished in that the elastic separating structure defines the partial volume in a gas-tight manner.
A disadvantage of these conventional heat recovery systems lies here in the long-term wear of the moving parts of the heat recovery system which are flowed around in such a way. In this respect, the named fluids have mostly physical characteristics with regard to density, viscosity, pour point, aniline point, dripping point and setting point and neutralization capacity, which show them to be of only limited suitability as lubricant. Also, the chemical compatibility with conventional drive components is not to be rated as non-critical in some of the heat carriers which are used. The tribological stress of the heat recovery system tends to be further intensified by the pressure level of the heat carrier necessary for operating the heat transfer device.